Some questions about the TRA & XP?

[shortstop20]

This is a post by winter brew from another thread, I have some questions so I thought I'd post them here.

The belt issues were caused by 2 things....POOR calibration and/or alignment being off.
Mostly the calibration. My riding buddy got a 163XP and just looking at the settup a guy that has tuned alot of TRA's could tell it would be a belt cooker. He changed his settup before he ever rode it and has not had a single belt problem. On the XP they went to a stiffer primary spring (less belt clamp), a steeper ramp (less belt clamp), lighter pin weight (les belt clamp), taller gearing and bigger drivers (more load on the clutches). this all adds up to alot of HEAT! Just throwing more pin weight and dropping the gearing would cure a large potion of the problems....instead they went with a different belt that is thicker and wider so there is more surface area for the sheaves to grip.....IMHO a shortcut fix, plus they can charge more for a belt.
just putting the '07 ramps, gearing down and adding pin weight will allow a guy to run the cheaper 166 and have no problems....with good alignment of course.
then there is the TRA wear issue....there is still no cure for this!

I know nothing about the TRA clutch....teach me.

pin weight?
what's the difference between the '07 and '08 ramps?
TRA wear issue? please explain.
The alignment has gotta be pretty easy to fix?

I am thinking about buying a slightly used/leftover 2008 before next winter. Leaning towards a Dragon 800 154" right now, might consider a Doo. I do not trust my dealer after seeing some of the work that he has done so I'd pretty much be on my own as far as fixing issues/tuning goes. Besides help from the SW forum of course.

 

[tollen77]

I'm gonna assume you know the basics of how a TRA clutch works... arms swing out further the higher the RPM is which move the sheaves and squeeze the belt. If you want to get more in depth just ask.

1) Pin weight is the adjustable weights that you can put in the arms of the TRA primary. The more weight you add the more belt squeeze you get, all other things being equal. The trade-off is that the motor must work harder to spin the extra weight. Usually not much of an issue as you generally want to add weight to the point you limit the peak RPM an engine can produce to the point that wide open throttle (WOT) has max RPM at the point where the engine produces max power.

2) Ramps are the curved part of the clutch that the arms push on as RPM increases. Adjusting the curvature of the ramps adjusts how much and when pressure is applied to the sheaves and thereby the belt.

3) The rollers on the TRA VII arms seem to wear out prematurely. Still working on the best aftermarket solution for this.

4) Alignment on a QRS secondary clutch is difficult to adjust as the secondary is attached to the jack shaft. In order to properly align the thing you have to add shims which involves taking the chain case apart as well as many other things. It is doable but not by someone without experience.


A couple things to note. The TRA design (the standard Doo clutch) is different from the P-85 design (the standard Polaris clutch as well as a similar design on many Yamahas). They do the same basic thing but do it differently. The main difference is where each clutch produces max belt squeeze for the sled. The more belt squeeze you have (to a point), the more power passes efficitnly from the engine past the clutches to the drive train and the snow.

The P-85 design produces less belt pinch at lower RPM's (where you do most of your accelerating) but a great deal of pinch at high RPM's (top speed). TRA clutches produces more belt pinch at low RPM's but less at top speed.

When making a decision between which sled - and clutch you want you should take into account what kind of sledding you do. Are you the kind that drives at WOT a great deal or the kind that is more of a boondocker that has a lot of quick bursts of accleration.


T